Normally, circuit arrangements for data stream distribution are designed according to the principle of “cross rail distribution”. In this context, data streams applied to one or more input connections are forwarded to one or more output connections.
Besides this unidirectional method, bidirectional methods are known which permit cross-rail distributor connections to act both as inputs and as outputs. The data streams to be forwarded—particularly bit data streams—exist in known protocols, for example in the known Ethernet V2/IEEE 802.3 protocol. Particularly in the case of bidirectional data stream transmission from one or more inputs/outputs to one or more outputs/inputs, conflicts can arise, since transmitting elements of a data stream precludes elements of a second data stream from being transmitted to the same output or from the same input at exactly the same time.
Great efforts have therefore been made to eliminate these input/output conflicts, and a number of methods have been proposed for this “conflict resolution” (contention resolution).
DE 19540160 describes a method for coordinating input-buffered ATM (Asynchronous Transfer Mode) switching centers in order to avoid output blockages. A cross rail distributor matrix operates in an entirely parallel manner, i.e. it switches a plurality of cells from different inputs to different outputs during the same interval of time. Since individual package transmissions by the system are normally entirely independent of one another, it is necessary to prevent a data cell from being connected to the same distributor rail matrix output during the same cell or slot period.
Conventional conflict resolution (contention resolution) is described in DE 19941851.9-31.
Apparatuses and methods for conflict resolution perform the following primary tasks, for example:                (a) Selection of data cells, with it being necessary to determine for each data cell period which data cells need to be connected from which inputs to individual cross-rail distributor matrix outputs. This subsidiary task of conflict resolution resolves any transmission conflicts for a plurality of inputs directed at the same distributor rail matrix output and has one or more of the following features:                    (i) Fairness: all of the inputs directed at the same output need to obtain the same share of the total throughput;            (ii) High throughput: the operation of conflict resolution and of its fairness algorithms should impair a total system throughput as little as possible;            (iii) Rapid manner of operation: since a new decision needs to be calculated for each data cell period, the calculation time required needs to be shorter than a cell slot time; and            (iv) Simple implementability: the conflict resolution unit needs to be able to be implemented as a synchronous finite state machine, with no asynchronous parts being allowed by the data-stream layout regulations; and                        (b) Buffer devices need to be provided in order to buffer data cells which are not forwarded during the current data cell period in order to be able to forward them as appropriate at a later time.        
The two tasks “selection” and “buffering” are thus of very great significance for data stream distribution and need to be performed by appropriate devices in the circuit arrangement.
DE 19935126.0 describes a cross rail distributor based system which contains an integrated conflict resolution unit. The task of selection is performed in a distributor device itself, while the task of buffering is performed on the basis of the prior art in the access units.
FIG. 5 shows a circuit arrangement for data stream distribution based on the prior art, where references starting with the digit “5” denote elements such as occur in circuit arrangements for data stream distribution and methods based on the prior art. One or more data stream lines are connected to first data stream connection units 504a-504n. Similarly, one or more data stream lines are connected to second data stream connection units 505a-505m. Both data stream connection units transmit data to and/or data from corresponding first access units 502a-502n and second access units 503a-503m.The first access units 502a-502n and the second access units 503a-503m are thus used both as inputs and as outputs for a central distributor device 500. The first access units 502a-502n and the second access units 503a-503m are connected to a matrix switching unit 501 contained in the distributor device 500.
For conflict resolution, it is necessary for the data streams supplied by first and second data stream connection units 504a-504n and 505a-505m not to be forwarded simultaneously to a single one of the corresponding output access units 502a-502n and 503a-503m in the same cell timeslot. For this reason, data are buffered in the first access units 502a-502n and in the second access units 503a-503m.The data stream distribution method in accordance with the prior art is based on data which cannot be forwarded to a desired access unit being buffered in the access unit at which the corresponding data stream arrives.
The information regarding whether or not a corresponding desired access unit is occupied is ascertained in the distributor device 500, so that relatively long information paths need to be provided between the respective first and second access units 502a-502n and 503a-503m and the matrix switching unit 501, since data are buffered in the access units 502a-502n and 503a-503m.Long information paths mean a long time delay which entails a problem in terms of short switching times. Such an arrangement based on the prior art is also described in DE 19935126.0, for example.
A primary drawback of such circuit arrangements for data stream distribution based on the prior art is that long information paths exist which in turn lengthen the switching times for the data streams.
Another drawback of apparatuses and methods for data stream distribution based on the prior art is that conventional conflict resolution limits the total data stream volume which can be transmitted.